1. Field of the Invention
The present invention relates to a communication apparatus having an automatic receiving function and a backup function of an image memory.
2. Related Background Art
In a prior art facsimile apparatus, a main power supply comprising a switching power supply is provided, and all systems of the main power supply are normally activated or limited systems are activated for stand-by. A primary circuit of the main power supply may be directly controlled by a call signal from a telephone line to save power consumption.
On the other hand, in the prior art facsimile apparatus, for back-up of a received image in case of power failure, a secondary battery is provided separately from the main power supply to supply power in case of power failure so that a controlling CPU and data retaining DRAM are activated by the secondary battery.
However, in the prior art facsimile apparatus having the switching power supply, the following problems are encountered because it always supplies power to a secondary circuit by the oscillation of the primary circuit of the main power supply.
(1) Power of approximately 10 watts is consumed in the stand-by mode. This power is consumed all day long for the automatic receiving function and the loss of power is very great.
(2) Radiation noise is generated because of (1), which may adversely affect other electronic equipment.
(3) It is practically difficult to directly control the primary circuit of the main power supply by a plurality of means because of severe safety regulation.
Further, the following problems are encountered in connection with the backup of the memory.
(4) Dedicated secondary backup battery and charging circuit for the secondary battery must be provided.
(5) The circuit board size increases because of (4).
(6) A considerable capacity of secondary battery is required to activate the CPU by the secondary battery and the time available for backup is short.
(7) The cost increases because of (4), (5) and (6).